Starting and operating circuit and device for electric discharge devices



STARTING AND OPERATING CIRCUIT AND DEVICE FOR ELECTRIC DISCHARGE DEVICES Filed June 29, 1948 y 1952 D c MILLER 2,597,591

4 Inverv-kor: David C. MiLLer', by W6 A His A=ttorfiey.

Patented May 20, 1952 HTED STATES STARTING AND OPERATING CIRCUIT AND DEVICE FOR ELECTRIC DISCHARGE DE- VICES David C. Miller, Cleveland Heights, Ohio, assignor to General Electric Company, a corporation of New York Application June 29, 1948, Serial No. 35,938

This invention relates to electric discharge devices of the type employing ionizable mediums such as gases or vapors, and more particularly to starting and operating devices and circuits therefor.

An object of my invention is to provide a new and improved starting and operating apparatus for electric discharge devices.

Another object of my invention is to provide a new and improved starting and operating circuit which will adequately start electric discharge lamps exposed to temperatures as low as F.

A further object of my invention is to provide a new and improved starting and operating circuit which will permit starting electric discharge lamps on voltages less than 12 volts.

A still further object of my invention is to provide a circuit for an electric discharge lamp operating on a 12 volt direct current supply which will permit a wide controlled variation of light output.

Further features and advantages or my invention will appear from the following detailed description of species thereof.

For a better understanding of my invention reference may be had to the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims. The drawing is a diagrammatic view of an electric discharge device and a starting and operating apparatus therefor embodying my invention.

Referring to the drawing, I have there illustrated one embodiment of my invention as applied to an electric discharge device I. The electric discharge device I, such as a fluorescent lamp, therein illustrated comprises a sealed glass envelope 2 containing a suitable ionizable medium. The envelope 2 may contain a fluorescent material, and it may be made of a vitreous ma terial which is transparent to ultraviolet rays where such radiation is to be utilized externally of the envelope. The ionizable medium may consist of a rare gas or a vaporizable material or mixtures thereof, for example, a mixture of argon and a small amount of mercury. The argon, for example, may be at a pressure of 0.5 to 8 millimeters Hg, preferably at a pressure of 3.5 to 4.5 millimeters. The envelope 2 contains a cathode 3 and an anode '4, the cathode 3 being mounted on lead-in conductors 5 and 6, and the anode 4 being mounted on a lead-in conductor i. The conductors '5, 6, and I extend through a conventional stem 8.

The cathode 3 is preferably a coiled-coil of wire having an overwind of finer wire thereon and coated with an electron-emissive material, preferably an alkaline earth oxide, or mixtures thereof, such as barium and strontium oxides. For the specific lamp shown in the drawing, which may be rated at about 3 watts, the cathode 4 Claims. (Cl. 315-94) 3 may be made to the following specifications: The cathode overwind wire may be tungsten having a diameter of 0.35 to 0.45 mils. This wire is wound at 400 turns per inch on a double mandrel of contiguous 2 mil tungsten and 2.5 mil molybdenum wires. This composite structure is then coiled on a 6 mil molybdenum mandrel at 44 turns per inch and the two molybdenum mandrel wires are subsequently removed. Obviously, there is an appreciable resistance between spaced points on the cathode coil.

The anode d is preferably made of a thin ribbon of nickel or molybdenum which, for the specific lamp referred to above, may be 4 millimeters wide, 5 mils thick and 25 millimeters long. As shown in the drawing, the anode 4 may be made substantially U-shaped, the bent portion having a diameter of about 3 millimeters, so that the distance between the outer surface of the coil cathode 3 and the inner surface of the anode 4 is less than 2 millimeters and preferably about 1 millimeter. Instead of making the anode 4 U-shaped, it may be made in the form of a cylinder. On the other hand, it may also be made in the form of a wire which may be merely an extension of the lead-in conductor 7. The ribbon form seems preferable in that it has a surface area of about 16 square millimeters facing the cathode 3.

As shown in the drawing, the lead 5 may be connected by means of a conductor 9 through a manual make-and-break switch 10 to the negative terminal ll of a suitable source of current supply H, H which may be a 12-16 volt storage battery. The lead I to the anode 4 is connected by means of a conductor l2 through a ballast inductance lt and a variable dimming resistance It to the positive terminal ll of the current supply. The inductance l3 may, for example, be a 15 ohm, 9 millihenries rated coil at a thousand cycles. The variable resistance M may comprise an element rated from 0-150 ohms. The lead 6 is connected by means of a conductor I5 through a resistance I 6 to the positive terminal ll of the current supply, Resistance It, for example, may bean element having 25 ohms resistance for supplying a continuous heating current to the cathode 3 during operation of device I. A switching means i! connects that portion of conductor 12 embodying inductance I3 and resistance 14 in parallel with that portion of conductor t5 embodying resistance l6; Switching means I7 is a normally ofi device which is on only when held in on position by the operator. It is desirable to have switching means I! and resistance It mechanically interconnected so that when switching means I! is placed in on position the resistance of I4 is at a minimum or zero value.

The starting and operating circuit illustrated in the drawing operates as follows: Upon closure of switch ill, cathode 3 is preheated to thezdesired electron-emitting temperature and is continually heated to this temperature as long as switch remains closed. Upon closure of switching means 11 current flows through switching means (1, inductance l3, and the variable dimming resistance [4. When variable dimming resistance I4 is set at its minimum value, either manually or by means of a mechanical interconnection with switch IT, with the choice of circuit elements which has been described, the current through the branch of the circuit comprising inductance I3 is appreciably greater than that flowing through resistance l6. Thus, when switching means I! is opened, the rate of change of current through inductance l3 produces a voltage impulse between cathode 3 and anode 4 which causes an arc discharge to occur therebetween. This voltage impulse is suflicient to cause an arc discharge to occur between the cathode and anode at starting voltages below I the normal line supply and at ambient temperatures at least as low as 20 F. The constant heating current supplied by the heating circuit 9, during operation of the lamp permits large range dimming at low operating ambient temperatures.

Under many operating conditions, the constant heating of the cathode allows automatic restart (i. e., without use of switching means [1) following momentary power failure.

While a specific embodiment has been shown and described, it will, of course, be understood that various modifications may be made without departing from the invention. Thus the values of circuit constants which have been given are purely illustrative and not in any sense limiting. It will be obvious that these may be modified in suitable manner for operation with low voltage fluorescent lamps having different operating requirements. The appended claims are, therefore, intended to cover any such modifications coming within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent is:

1. Apparatus for operating an electric discharge device of the type including a filamentary thermionic cathode and an anode, comprising: said device; a unidirectional voltage source, and a resistor, a heating circuit for said cathode constituted by connecting it, in series with said resistor, across said source; a main discharge circuit including the cathode-to-anode path of said device, an inductance, and a variable resistance, connected in series across said source; and a normally open switch, connected to place said variable resistance and inductance in parallel with said first-named resistor when operated, the reopening of said switch after operation providing an inductive voltage surge through said inductance for starting a discharge within said device.

2. Apparatus for operating an electric discharge lamp of the type including a filamentary thermionic cathode and an anode, comprising: said lamp, a low voltage unidirectional source, and a limiting resistance; a heating circuit for said cathode constituted by connecting it, in series with said limiting resistance, across said source; a main discharge circuit for obtaining an adjustable radiant output from said lamp and including the cathode-to-anode path thereof, an inductance and a variable resistance connected in series across said source; and a normally open switch forconnecting' said inductance in parallel with said limiting resistance in order to permit the heating current for said cathode to flow through said inductance when said switch is closed, the voltage induced in said inductance upon reopening of said switch producing an impulse at said anode for starting a discharge within said lamp.

3. Apparatus for operating an electric discharge device of the type including a filamentary thermionic cathode and an anode, comprising: said device, a unidirectional voltage source, and a limiting resistance; a heating circuit for said cathode, constituted by connecting one filamentary end thereof to the negative side of said source and the other filamentary end thereof, in series with said limiting resistance, to the positive side of said source; a discharge circuit including said anode, an inductance and a variable resistance, serially connected to the positive side of said source, adjustment of said variable resistance permitting control of the discharge current through said device; and a normally open switch connected between the junction of said limiting resistance with said filamentary end, and the junction of said inductance with said anode, said switch, when closed, permitting cathode heating current to flow through said inductance, so that the voltage induced therein upon reopening of said switch is available at said anode for starting a discharge within said device.

4. Apparatus for operating an electric discharge lamp of the type including a filamentary thermionic cathode and an anode, comprising: said lamp, a unidirectional voltage source, and a limiting resistance; a heating circuit for said cathode constituted by connecting one filamentary end thereof to the negative side of said source, and the other filamentary end thereof, in series with said limiting resistance, to the positive side of said source; a discharge circuit including said anode, an inductance and a variable resistance, serially connected to the positive side of said source, adjustment of said resistance permitting control of the radiant output from said lamp; a normally open switch connected between the junction of said limiting resistance with said filamentary end, and the junction of said inductance with said anode, said switch having a mechanical linkage with said variable resistance such that it closes when said variable resistance is set at its minimum value, said switch, when closed, permitting the cathode heating current to flow through said inductance so that the voltage induced therein upon reopening of said switch is available at said anode for starting a discharge within said lamp.

DAVID C. MILLER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Re. 22,503 Campbell June 27, 1944 2,058,950 Bruijnes Oct. 27, 1936 2,241,360 Gaynor May 6, 1941 2,337,746 Garstang Dec. 28, 1943 2,394,966 Floyd Feb. 12, 1946 FOREIGN PATENTS Number Country Date 533,422 Great Britain Feb. 12, 1941 

